0
0.0

Jun 30, 2018
06/18

by
Johannes Richter; Oliver Götze

texts

######
eye 0

######
favorite 0

######
comment 0

The existence of a spin-liquid ground state of the $s=1/2$ Heisenberg kagome antiferromagnet (KAFM) is well established. Meanwhile, also for the $s=1$ Heisenberg KAFM evidence for the absence of magnetic long-range order (LRO) was found. Magnetic LRO in Heisenberg KAFMs can emerge by increasing the spin quantum number $s$ to $s>1$ and for $s=1$ by an easy-plane anisotropy. In the present paper we discuss the route to magnetic order in $s=1/2$ KAFMs by including an isotropic interlayer...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1704.06809

31
31

Sep 19, 2013
09/13

by
Oleg Derzhko; Johannes Richter

texts

######
eye 31

######
favorite 0

######
comment 0

We consider the quantum spin-$s$ $XXZ$ Heisenberg antiferromagnet on the two- and three-dimensional pyrochlore lattices and examine a spin-Peierls mechanism of lowering the total energy by a lattice distortion in a high magnetic field. For the exact eigenstates consisting of several independent localized magnons in a ferromagnetic environment we show the existence of a spin-Peierls instability by rigorous analytical calculations. In addition we report on exact diagonalization data for finite...

Source: http://arxiv.org/abs/cond-mat/0507538v1

31
31

Sep 20, 2013
09/13

by
Oleg Derzhko; Johannes Richter

texts

######
eye 31

######
favorite 0

######
comment 0

For a class of highly frustrated antiferromagnetic quantum spin lattices the ground state exhibits a huge degeneracy in high magnetic fields due to the existence of localized magnon states. For some of these spin lattices (in particular, the 1D dimer-plaquette, sawtooth and kagom\'{e}-like chains as well as the 2D kagom\'{e} lattice) we calculate rigorously the ground-state entropy at the saturation field. We find that the ground-state entropy per site remains finite at saturation. This...

Source: http://arxiv.org/abs/cond-mat/0404204v1

2
2.0

Jun 29, 2018
06/18

by
Johannes Richter; Oleg Derzhko

texts

######
eye 2

######
favorite 0

######
comment 0

To illustrate a simple mean-field-like approach for examining quantum phase transitions we consider the $J-J^\prime$ quantum Heisenberg antiferromagnet on a square lattice. The exchange couplings $J$ and $J^\prime$ are competing with each other. The ratio $J^\prime/J$ is the control parameter and its change drives the transition. We adopt a variational ansatz, calculate the ground-state energy as well as the order parameter and describe the quantum phase transition inherent in the model. This...

Topics: Statistical Mechanics, Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1611.09655

36
36

Sep 23, 2013
09/13

by
Piotr Tomczak; Johannes Richter

texts

######
eye 36

######
favorite 0

######
comment 0

We investigate the critical parameters of an order-disorder quantum phase transitions in the spin-1/2 $J-J'$ Heisenberg and XY antiferromagnets on square lattice. Basing on the excitation gaps calculated by exact diagonalization technique for systems up to 32 spins and finite-size scaling analysis we estimate the critical couplings and exponents of the correlation length for both models. Our analysis confirms the universal critical behavior of these quantum phase transitions: They belong to 3D...

Source: http://arxiv.org/abs/cond-mat/0109108v2

40
40

Sep 22, 2013
09/13

by
Andreas Voigt; Johannes Richter

texts

######
eye 40

######
favorite 0

######
comment 0

We consider the frustrated antiferromagnetic s=1 Heisenberg quantum spin chain with regard to the Marshall-Peierls sign rule (MPSR). By using exact diagonalization data we investigate the breakdown of the MPSR in dependence on frustration and compare our findings with data for s=1/2. We calculate a critical value of frustration J_2(crit) where the MPSR is violated. The extrapolation of this value to the infinite chain limit holds J_2(crit) approx. 0.016, lower than in the case of s=1/2...

Source: http://arxiv.org/abs/cond-mat/0003207v1

0
0.0

Jun 30, 2018
06/18

by
Oleg Derzhko; Johannes Richter

texts

######
eye 0

######
favorite 0

######
comment 0

We investigate a mechanism to establish ground-state ferromagnetism in flat-band Hubbard systems based on a kind of {\it order-from-disorder} effect driven by dispersion. As a paradigm we consider a frustrated diamond chain, where for ideal diamond geometry the lowest one-electron band is flat, but the ground state remains paramagnetic for arbitrary on-site repulsion $U$. We focus on half filling of the flat band. By using numerical and analytical arguments we present the ground-state phase...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1404.2230

10
10.0

Jan 11, 2020
01/20

by
Sviatoslav Richter; Johannes Brahms

audio

######
eye 10

######
favorite 0

######
comment 0

Tracklist: 1. Piano Sonata No. 1 in C major, Op. 1: I. Allegro - - Johannes Brahms 2. Piano Sonata No. 1 in C major, Op. 1: II. Andante - Johannes Brahms 3. Piano Sonata No. 1 in C major, Op. 1: III. Scherzo: Allegro molto e con fuoco - Johannes Brahms 4. Piano Sonata No. 1 in C major, Op. 1: IV. Finale: Allegro con fuoco - Johannes Brahms 5. Piano Sonata No. 2 in F-sharp minor, Op. 2: I. Allegro non troppo ma energico - Johannes Brahms 6. Piano Sonata No. 2 in F-sharp minor, Op. 2: II. Andante...

Topic: Other Classical

Source: CD

35
35

Sep 20, 2013
09/13

by
Oleg Derzhko; Johannes Richter

texts

######
eye 35

######
favorite 0

######
comment 0

We extend the consideration of the spin-1/2 transverse XY chain with correlated Lorentzian disorder (Phys. Rev. B {\bf 55,} 14298 (1997)) for the case of additional Dzyaloshinskii-Moriya interspin interaction. It is shown how the averaged density of states can be calculated exactly. Results are presented for the density of states and the transverse magnetization.

Source: http://arxiv.org/abs/cond-mat/9810143v1

Title Neue Jahrbuecher fuer das klassische Altertum, Geschichte und deutsche Literatur und fÃ¼r Paedagogik, Volume 4 Editors Johannes Ilberg, Richard Immanuel Richter, Bernhard Gerth, Paul Cauer Publisher Leipzig: B. G. Teubner., 1899 source http://books.google.com/books?id=JLgNAAAAYAAJ

Topics: History (Germany), Books by FK

52
52

Jul 20, 2013
07/13

by
Oleg Derzhko; Johannes Richter

texts

######
eye 52

######
favorite 0

######
comment 0

We study the low-temperature thermodynamic properties of a number of frustrated quantum antiferromagnets which support localized magnon states in the vicinity of the saturation field. For this purpose we use 1) a mapping of the low-energy degrees of freedom of spin systems onto the hard-core object lattice gases and 2) an exact diagonalization of finite spin systems of up to N=30 sites. The considered spin systems exhibit universal behavior which is determined by a specific hard-core object...

Source: http://arxiv.org/abs/cond-mat/0604023v1

53
53

Jul 22, 2013
07/13

by
Oleg Derzhko; Johannes Richter

texts

######
eye 53

######
favorite 0

######
comment 0

One random spin-1/2 XY chain that after Jordan-Wigner fermionization reduces to the extended Lloyd's model is considered. The random-averaged one-fermion Green functions have been calculated exactly that yields thermodynamics of the spin model.

Source: http://arxiv.org/abs/cond-mat/9702004v1

1
1.0

Jun 28, 2018
06/18

by
Oliver Götze; Johannes Richter

texts

######
eye 1

######
favorite 0

######
comment 0

While the existence of a spin-liquid ground state of the spin-1/2 kagome Heisenberg antiferromagnet (KHAF) is well established, the discussion of the effect of an interlayer coupling (ILC) by controlled theoretical approaches is still lacking. Here we study this problem by using the coupled-cluster method to high orders of approximation. We consider a stacked KHAF with a perpendicular ILC $J_\perp$, where we study ferro- as well as antiferromagnetic $J_\perp$. We find that the spin-liquid...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1510.04898

52
52

Sep 23, 2013
09/13

by
Heinz-Jürgen Schmidt; Johannes Richter

texts

######
eye 52

######
favorite 0

######
comment 0

We consider a class of geometrically frustrated Heisenberg spin systems which admit exact ground states. The systems consist of suitably coupled antiferromagnetic spin trimers with integer spin quantum numbers $s$ and their ground state $\Phi$ will be the product state of the local singlet ground states of the trimers. We provide linear equations for the inter-trimer coupling constants which are equivalent to $\Phi$ being an eigenstate of the corresponding Heisenberg Hamiltonian and sufficient...

Source: http://arxiv.org/abs/1006.4299v2

44
44

Sep 23, 2013
09/13

by
Johannes Richter; Heinz-Jürgen Schmidt

texts

######
eye 44

######
favorite 0

######
comment 0

We consider a two-dimensional geometrically frustrated integer-spin Heisenberg system that admits an exact ground state. The system corresponds to a decorated square lattice with two coupling constants J1 and J2, and it can be understood as a generalized Shastry-Sutherland model. Main elements of the spin model are suitably coupled antiferromagnetic spin trimers with integer spin quantum numbers s and their ground state Phi will be the product state of the local singlet ground states of the...

Source: http://arxiv.org/abs/1202.5854v1

34
34

Sep 21, 2013
09/13

by
Sven E. Krüger; Johannes Richter

texts

######
eye 34

######
favorite 0

######
comment 0

We study a square-lattice spin-half Heisenberg model where frustration is introduced by competing nearest-neighbor bonds of different signs. We discuss the influence of quantum fluctuations on the nature of the zero-temperature phase transitions from phases with collinear magnetic order at small frustration to phases with noncollinear spiral order at large frustration. We use the coupled cluster method (CCM) for high orders of approximation (up to LSUB6) and the exact diagonalization of finite...

Source: http://arxiv.org/abs/cond-mat/0104540v1

40
40

Sep 23, 2013
09/13

by
Volodymyr Derzhko; Oleg Derzhko; Johannes Richter

texts

######
eye 40

######
favorite 0

######
comment 0

We present exact results for the ground-state and thermodynamic properties of the spin-1/2 $XX$ chain with three-site interactions in a random (Lorentzian) transverse field. We discuss the influence of randomness on the quantum critical behavior known to be present in the nonrandom model. We find that at zero temperature the characteristic features of the quantum phase transition, such as kinks in the magnetization versus field curve, are smeared out by randomness. However, at low but finite...

Source: http://arxiv.org/abs/1012.2058v2

65
65

Sep 24, 2013
09/13

by
Heinz-Jürgen Schmidt; Andre Lohmann; Johannes Richter

texts

######
eye 65

######
favorite 0

######
comment 0

We explicitly calculate the moments $t_n$ of general Heisenberg Hamiltonians up to eighth order. They have the form of finite sums of products of two factors. The first factor is represented by a (multi-)graph which has to be evaluated for each particular system under consideration. The second factors are well-known universal polynomials in the variable $s(s+1)$, where $s$ denotes the individual spin quantum number. From these moments we determine the corresponding coefficients of the...

Source: http://arxiv.org/abs/1112.0953v1

50
50

Sep 19, 2013
09/13

by
Oleg Derzhko; Taras Krokhmalskii; Johannes Richter

texts

######
eye 50

######
favorite 0

######
comment 0

Based on exact diagonalization data for finite quantum Heisenberg antiferromagnets on two frustrated lattices (two-leg ladder and bilayer) and analytical arguments we map low-energy degrees of freedom of the spin models in a magnetic field on classical lattice-gas models. Further we use transfer-matrix calculations and classical Monte Carlo simulations to give a quantitative description of low-temperature thermodynamics of the quantum spin models. The classical lattice-gas model yields an...

Source: http://arxiv.org/abs/1009.3828v1

77
77

Jul 20, 2013
07/13

by
Heinz-Jürgen Schmidt; Johannes Richter; Roderich Moessner

texts

######
eye 77

######
favorite 0

######
comment 0

At the magnetic saturation field, certain frustrated lattices have a class of states known as "localized multi-magnon states" as exact ground states. The number of these states scales exponentially with the number $N$ of spins and hence they have a finite entropy also in the thermodynamic limit $N\to \infty$ provided they are sufficiently linearly independent. In this article we present rigorous results concerning the linear dependence or independence of localized magnon states and...

Source: http://arxiv.org/abs/cond-mat/0604649v1

30
30

Sep 18, 2013
09/13

by
Ronald Zinke; Joerg Schulenburg; Johannes Richter

texts

######
eye 30

######
favorite 0

######
comment 0

We investigate the ground-state magnetic long-range order of quasi-one-dimensional quantum Heisenberg antiferromagnets for spin quantum numbers s=1/2 and s=1. We use the coupled cluster method to calculate the sublattice magnetization in dependence on the inter-chain coupling. We find that for the unfrustrated spin-1/2 system an infinitesimal inter-chain coupling is sufficient to stabilize magnetic long-range order, which is in agreement with results obtained by some other methods. For s=1 we...

Source: http://arxiv.org/abs/0705.3582v2

38
38

Sep 23, 2013
09/13

by
Heinz-Juergen Schmidt; Andre Lohmann; Johannes Richter

texts

######
eye 38

######
favorite 0

######
comment 0

We explicitly calculate the moments t_n of general Heisenberg Hamiltonians up to sixth order. They have the form of finite sums of products of two factors, the first factor being represented by a multigraph and the second factor being a polynomial in the variable s(s + 1), where s denotes the individual spin quantum number. As an application we determine the corresponding coefficients of the expansion of the free energy and the zero field susceptibility in powers of the inverse temperature....

Source: http://arxiv.org/abs/1012.4166v3

34
34

Sep 21, 2013
09/13

by
Mykola Maksymenko; Oleg Derzhko; Johannes Richter

texts

######
eye 34

######
favorite 0

######
comment 0

We consider the antiferromagnetic Heisenberg and the repulsive Hubbard model on two $N$-site one-dimensional lattices, which support dispersionless one-particle states corresponding to localized states on triangular trapping cells. We calculate the degeneracy of the ground states in the subspaces with $n\le n_{\max}$, $n_{\max}\propto N$ magnons or electrons as well as the contribution of these states (independent localized states) to thermodynamic quantities. Moreover, we discuss another class...

Source: http://arxiv.org/abs/1108.5453v1

12
12

Jan 23, 2020
01/20

by
Robert Schumann; Johannes Brahms; Sviatoslav Richter

audio

######
eye 12

######
favorite 0

######
comment 0

Tracklist: 1. Bunte Blätter, Op. 99 (Beginning): Drei Stücklein 2. Bunte Blätter, Op. 99 (Beginning): Fünf Albumblätter 3. Bunte Blätter, Op. 99 (Beginning): Novellette 4. Bunte Blätter, Op. 99 (Beginning): Präludium 5. Bunte Blätter, Op. 99 (Beginning): Marsch 6. Bunte Blätter, Op. 99 (Conclusion): Abendmusik 7. Bunte Blätter, Op. 99 (Conclusion): Scherzo 8. Bunte Blätter, Op. 99 (Conclusion): Geschwindmarsch 9. From Klavierstücke, Op. 118: Intermezzo In C Major, No. 1 10. From...

Topics: Classical, Romantic

Source: Vinyl LP

95
95

Jul 22, 2013
07/13

by
Ronald Zinke; Stefan-Ludwig Drechsler; Johannes Richter

texts

######
eye 95

######
favorite 0

######
comment 0

We investigate the influence of an inter-chain coupling on the spiral ground state correlations of a spin-1/2 Heisenberg model consisting of a two-dimensional array of coupled chains with nearest (J1) and frustrating next-nearest neighbor (J2) in-chain exchange couplings. Using the coupled-cluster method we calculate the transition point between the commensurate and the incommensurate (spiral) ground state as well as the quantum pitch angle of the spiral ground state. In addition, we provide a...

Source: http://arxiv.org/abs/0807.3431v2

112
112

Sep 22, 2013
09/13

by
Sven E. Krueger; Dirk Schmalfuss; Johannes Richter

texts

######
eye 112

######
favorite 0

######
comment 0

While the diagonalization of a quadratic bosonic form can always be done using a Bogoliubov transformation, the practical implementation for systems with a large number of different bosons is a tedious analytical task. Here we use the coupled cluster method (CCM) to exactly diagonalise such complicated quadratic forms. This yields to a straightforward algorithm which can easily be implemented using computer algebra even for a large number of different bosons. We apply this method on a...

Source: http://arxiv.org/abs/cond-mat/0003105v1

96
96

Jul 24, 2013
07/13

by
Oleg Derzhko; Andreas Honecker; Johannes Richter

texts

######
eye 96

######
favorite 0

######
comment 0

We study the repulsive Hubbard model both analytically and numerically on a family of highly frustrated lattices which have one-electron states localized on isolated trapping cells. We construct and count exact many-electron ground states for a wide range of electron densities and obtain closed-form expressions for the low-temperature thermodynamic quantities. Furthermore, we find that saturated ferromagnetism is obtained only for sufficiently high electron densities and large Hubbard repulsion...

Source: http://arxiv.org/abs/0807.2991v2

61
61

Sep 22, 2013
09/13

by
Oleg Derzhko; Johannes Richter; Taras Verkholyak

texts

######
eye 61

######
favorite 0

######
comment 0

Using the two-dimensional Jordan-Wigner fermionization we calculate the thermodynamic quantities of the (spatially anisotropic) square-lattice spin-1/2 anisotropic XY (XZ) model. We compare the results of different approaches for the ground-state and thermodynamic properties of the model.

Source: http://arxiv.org/abs/cond-mat/0111203v1

43
43

Sep 23, 2013
09/13

by
Oleg Derzhko; Johannes Richter; Jörg Schulenburg

texts

######
eye 43

######
favorite 0

######
comment 0

We study the stability of some strongly frustrated antiferromagnetic spin lattices in high magnetic fields against lattice distortions. In particular, we consider a spin-s anisotropic Heisenberg antiferromagnet on the square-kagom\'{e} and kagom\'{e} lattices. The independent localized magnons embedded in a ferromagnetic environment, which are the ground state at the saturation field, imply lattice instabilities for appropriate lattice distortions fitting to the structure of the localized...

Source: http://arxiv.org/abs/cond-mat/0510582v1

0
0.0

Jun 29, 2018
06/18

by
Patrick Müller; Johannes Richter; Oleg Derzhko

texts

######
eye 0

######
favorite 0

######
comment 0

We consider the standard repulsive Hubbard model with a flat lowest-energy band for two one-dimensional lattices (diamond chain and ladder) as well as for a two-dimensional lattice (bilayer) at half filling of the flat band. The considered models do not fall in the class of Mielke-Tasaki flat-band ferromagnets, since they do not obey the connectivity conditions. However, the ground-state ferromagnetism can emerge, if the flat band becomes dispersive. To study this kinetic-energy-driven...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1602.00439

31
31

Sep 18, 2013
09/13

by
Johannes Richter; Oleg Derzhko; Taras Krokhmalskii

texts

######
eye 31

######
favorite 0

######
comment 0

We investigate the thermodynamic properties of the frustrated bilayer quantum Heisenberg antiferromagnet at low temperatures in the vicinity of the saturation magnetic field. The low-energy degrees of freedom of the spin model are mapped onto a hard-square gas on a square lattice. We use exact diagonalization data for finite spin systems to check the validity of such a description. Using a classical Monte Carlo method we give a quantitative description of the thermodynamics of the spin model at...

Source: http://arxiv.org/abs/cond-mat/0606806v1

39
39

Sep 19, 2013
09/13

by
Oleg Derzhko; Johannes Richter; Oles' Zaburannyi

texts

######
eye 39

######
favorite 0

######
comment 0

Using the Jordan-Wigner fermionization, Green function approach and continued fractions we examine rigorously the local magnetizations and the local static susceptibilities of the spin-1/2 XX chain in a transverse field with regularly varying exchange interactions. We discuss our findings from a viewpoint of the strong-coupling approach.

Source: http://arxiv.org/abs/cond-mat/0010120v1

29
29

Sep 18, 2013
09/13

by
Oleg Derzhko; Johannes Richter; Oles' Zaburannyi

texts

######
eye 29

######
favorite 0

######
comment 0

Using the Jordan-Wigner transformation and the continued-fraction method we calculate exactly the density of states and thermodynamic quantities of the periodic nonuniform spin-1/2 isotropic XY chain in a transverse field. We discuss in detail the changes in the behaviour of the thermodynamic quantities caused by regular nonuniformity. The exact consideration of thermodynamics is extended including a random Lorentzian transverse field. The presented results are used to study the Peierls...

Source: http://arxiv.org/abs/cond-mat/0002136v1

5
5.0

Jun 26, 2018
06/18

by
Oleg Derzhko; Johannes Richter; Mykola Maksymenko

texts

######
eye 5

######
favorite 0

######
comment 0

In this review we recapitulate the basic features of the flat-band spin systems and briefly summarize earlier studies in the field. Main emphasis is made on recent developments which include results for both spin and electron flat-band models. In particular, for flat-band spin systems we highlight field-driven phase transitions for frustrated quantum Heisenberg antiferromagnets at low temperatures, chiral flat-band states, as well as the effect of a slight dispersion of a previously strictly...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1502.02729

30
30

Sep 23, 2013
09/13

by
Oleg Derzhko; Johannes Richter; Oles' Zaburannyi

texts

######
eye 30

######
favorite 0

######
comment 0

We use continued fractions for a study of the thermodynamic properties of the periodic nonuniform spin-1/2 isotropic XY chain in a non-random/random (Lorentzian) transverse field. The obtained results permit to examine the influence of a magnetic field and randomness on the spin-Peierls dimerization.

Source: http://arxiv.org/abs/cond-mat/9909251v1

34
34

Sep 23, 2013
09/13

by
Johannes Richter; Oleg Derzhko; J/"org Schulenburg

texts

######
eye 34

######
favorite 0

######
comment 0

For a class of frustrated antiferromagnetic spin lattices (in particular, the square-kagom\'{e} and kagom\'{e} lattices) we discuss the impact of recently discovered exact eigenstates on the stability of the lattice against distortions. These eigenstates consist of independent localized magnons embedded in a ferromagnetic environment and become ground states in high magnetic fields. For appropriate lattice distortions fitting to the structure of the localized magnons the lowering of magnetic...

Source: http://arxiv.org/abs/cond-mat/0312216v2

5
5.0

Jan 7, 2020
01/20

by
Sviatoslav Richter; Johannes Brahms; Franz Liszt

audio

######
eye 5

######
favorite 0

######
comment 0

Tracklist: 1. Brahms: Piano Sonata #1 In C, Op. 1 - 1. Allegro 2. Brahms: Piano Sonata #1 In C, Op. 1 - 2. Andante 3. Brahms: Piano Sonata #1 In C, Op. 1 - 3. Scherzo: Allegro Molto E Con Fuoco 4. iV. Finale - Allegro con fuoco 5. Consolation No. 6 6. Hungarian Rhapsody No. 17 7. Harmonies du Soir [Etudes d'execution transcentante] 8. Scherzo & March - Scherzo 9. March

Topic: Other Classical

Source: CD

36
36

Sep 19, 2013
09/13

by
Oleg Derzhko; Andreas Honecker; Johannes Richter

texts

######
eye 36

######
favorite 0

######
comment 0

The repulsive Hubbard model on a sawtooth chain exhibits a lowest single-electron band which is completely dispersionless (flat) for a specific choice of the hopping parameters. We construct exact many-electron ground states for electron fillings up to 1/4. We map the low-energy degrees of freedom of the electron model to a model of classical hard dimers on a chain and, as a result, obtain the ground-state degeneracy as well as closed-form expressions for the low-temperature thermodynamic...

Source: http://arxiv.org/abs/cond-mat/0703295v2

114
114

Sep 17, 2013
09/13

by
Andreas Voigt; Johannes Richter; Piotr Tomczak

texts

######
eye 114

######
favorite 0

######
comment 0

We present an exact diagonalization study of the quantum Heisenberg antiferromagnet on the fractal Sierpinski gasket for spin quantum numbers s=1/2,s=1 and s=3/2. Since the fractal dimension of the Sierpinski gasket is between one and two we compare the results with corresponding data of one- and two-dimensional systems. By analyzing the ground-state energy, the low-lying spectrum, the spin-spin correlation and the low-temperature thermodynamics we find arguments, that the Heisenberg...

Source: http://arxiv.org/abs/cond-mat/0108472v1

41
41

Sep 22, 2013
09/13

by
Oleg Derzhko; Taras Krokhmalskii; Johannes Richter

texts

######
eye 41

######
favorite 0

######
comment 0

Using a lattice-gas description of the low-energy degrees of freedom of the quantum Heisenberg antiferromagnet on the frustrated two-leg ladder and bilayer lattices we examine the magnetization process at low temperatures for these spin models. In both cases the emergent discrete degrees of freedom implicate a close relation of the frustrated quantum Heisenberg antiferromagnet to the classical lattice gas with finite nearest-neighbor repulsion or, equivalently, to the Ising antiferromagnet in a...

Source: http://arxiv.org/abs/1103.5124v1

0
0.0

Jun 29, 2018
06/18

by
Johannes Richter; Patrick Müller; Andre Lohmann; Heinz-Jürgen Schmidt

texts

######
eye 0

######
favorite 0

######
comment 0

We present the high-temperature expansion up to 11th order for the specific heat $C$ and the uniform susceptibility $\chi_0$ and up to 9th order for the structure factor $S_{\bf Q}$ of the frustrated spin-half $J_1$-$J_2$ Heisenberg model on the BCC lattice. We consider ferromagnetic as well as antiferromagnetic nearest-neighbor exchange $J_1$ and frustrating antiferromagnetic next-nearest-neighbor exchange $J_2$. We discuss the influence of frustration on the temperature dependence of these...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1609.06837

12
12

Feb 4, 2020
02/20

by
Sviatoslav Richter; Carl Maria von Weber; Johannes Brahms; Sergei Prokofiev

audio

######
eye 12

######
favorite 0

######
comment 0

Tracklist: 1. Sonata No. 3 in D minor: I. Allegro feroce - Carl Maria von Weber 2. Sonata No. 3 in D minor: II. Andante con motto - Carl Maria von Weber 3. Sonata No. 3 in D minor: III. Rondò (presto) - Carl Maria von Weber 4. Cappricio in C major Op. 76 No. 8 - Johannes Brahms 5. Intermezzo in E minor Op. 116 No. 5 - Johannes Brahms 6. Ballade in E minor Op. 118 No. 3 - Johannes Brahms 7. Rhaposdy in E flat major Op. 119 No. 4 - Johannes Brahms 8. Sonata No. 6 in A major Op. 82: II. Allegro...

Source: CD

12
12

Jan 17, 2020
01/20

by
Sviatoslav Richter; Schumann; Brahms; Johannes Brahms; Robert Schumann

audio

######
eye 12

######
favorite 0

######
comment 0

Tracklist: Disc 1: 1. Piano Sonata No. 1 in C Op. 1: I. Allegro - Johannes Brahms 2. Piano Sonata No. 1 in C Op. 1: II. Andante - Johannes Brahms 3. Piano Sonata No. 1 in C Op. 1: III. Scherzo. Allegro molto e con fuoco - Johannes Brahms 4. Piano Sonata No. 1 in C Op. 1: IV. Finale. Allegro con fuoco - Johannes Brahms 5. Piano Sonata No. 2 in F sharp minor Op. 2: I. Allegro non troppo, ma energico - Johannes Brahms 6. Piano Sonata No. 2 in F sharp minor Op. 2: II. Andante con espressione -...

Source: CD

74
74

Jul 20, 2013
07/13

by
M. D. Johannes; J. Richter; S. -L. Drechsler; H. Rosner

texts

######
eye 74

######
favorite 0

######
comment 0

We present evidence that crystalline Sr_2Cu(PO_4)_2 is a nearly perfect one-dimensional (1D) spin-1/2 anti-ferromagnetic Heisenberg model (AHM) chain compound with nearest neighbor only exchange. We undertake a broad theoretical study of the magnetic properties of this compound using first principles (LDA, LDA+U calculations), exact diagonalization and Bethe-ansatz methodologies to decompose the individual magnetic contributions, quantify their effect, and fit to experimental data. We calculate...

Source: http://arxiv.org/abs/cond-mat/0609430v1

49
49

Sep 19, 2013
09/13

by
Ravindra W. Chhajlany; Piotr Tomczak; Antoni Wojcik; Johannes Richter

texts

######
eye 49

######
favorite 0

######
comment 0

We present an analysis of the entanglement characteristics in the Majumdar-Ghosh (MG) or $J_{1}$-$J_{2}$ Heisenberg model. For a system consisting of up to 28 spins, there is a deviation from the scaling behaviour of the entanglement entropy characterizing the unfrustrated Heisenberg chain as soon as $J_{2} >0.25$. This feature can be used as an indicator of the dimer phase transition that occurs at $J_{2} = J_{2}^{*} \approx 0.2411 J_{1}$. Additionally, we also consider entanglement at the...

Source: http://arxiv.org/abs/cond-mat/0610379v1

38
38

Sep 22, 2013
09/13

by
Andreas Honecker; Shijie Hu; Robert Peters; Johannes Richter

texts

######
eye 38

######
favorite 0

######
comment 0

The natural mineral azurite Cu3(CO3)2(OH)2 is an interesting spin-1/2 quantum antiferromagnet. Recently, a generalised diamond chain model has been established as a good description of the magnetic properties of azurite with parameters placing it in a highly frustrated parameter regime. Here we explore further properties of this model for azurite. First, we determine the inelastic neutron scattering spectrum in the absence of a magnetic field and find good agreement with experiments, thus...

Source: http://arxiv.org/abs/1103.1080v1

62
62

Jul 20, 2013
07/13

by
Oleg Derzhko; Johannes Richter; Olesia Krupnitska; Taras Krokhmalskii

texts

######
eye 62

######
favorite 0

######
comment 0

We consider the spin-1/2 antiferromagnetic Heisenberg model on three frustrated lattices (the diamond chain, the dimer-plaquette chain and the two-dimensional square-kagome lattice) with almost dispersionless lowest magnon band. Eliminating high-energy degrees of freedom at high magnetic fields, we construct low-energy effective Hamiltonians which are much simpler than the initial ones. These effective Hamiltonians allow a more extended analytical and numerical analysis. In addition to the...

Source: http://arxiv.org/abs/1304.4136v1

33
33

Sep 23, 2013
09/13

by
Oleg Derzhko; Johannes Richter; Taras Krokhmalskii; Oles' Zaburannyi

texts

######
eye 33

######
favorite 0

######
comment 0

Using the Jordan-Wigner transformation and continued fractions we calculate rigorously the thermodynamic quantities for the spin-1/2 transverse Ising chain with periodically varying intersite interactions and/or on-site fields. We consider in detail the properties of the chains having a period of the transverse field modulation equal to 3. The regularly alternating transverse Ising chain exhibits several quantum phase transition points, where the number of transition points for a given period...

Source: http://arxiv.org/abs/cond-mat/0408033v1

1
1.0

Jun 30, 2018
06/18

by
Johannes Broedel; Nils Matthes; Gregor Richter; Oliver Schlotterer

texts

######
eye 1

######
favorite 0

######
comment 0

We consider a generalization of elliptic multiple zeta values, which we call twisted elliptic multiple zeta values. These arise as iterated integrals on an elliptic curve from which a rational lattice has been removed. At the cusp, twisted elliptic multiple zeta values are shown to degenerate to cyclotomic multiple zeta values in the same way as elliptic multiple zeta values degenerate to classical multiple zeta values. We investigate properties of twisted elliptic multiple zeta values and...

Topics: High Energy Physics - Theory, Number Theory, Mathematics

Source: http://arxiv.org/abs/1704.03449

48
48

Sep 22, 2013
09/13

by
Taras Verkholyak; Jozef Strecka; Michal Jascur; Johannes Richter

texts

######
eye 48

######
favorite 0

######
comment 0

The Jordan-Wigner transformation is applied to study magnetic properties of the quantum spin-1/2 $XX$ model on the diamond chain. Generally, the Hamiltonian of this quantum spin system can be represented in terms of spinless fermions in the presence of a gauge field and different gauge-invariant ways of assigning the spin-fermion transformation are considered. Additionally, we analyze general properties of a free-fermion chain, where all gauge terms are neglected and discuss their relevance for...

Source: http://arxiv.org/abs/1004.0848v4